What is the difference between decimal, float and double in .NET?
When would someone use one of these?
2209
votes
interesting article zetcode.com/lang/csharp/datatypes
– GibboK
Related: sandbox.mc.edu/~bennet/cs110/flt/dtof.html
– Pacerier
You cannot use decimal to interop with native code since it is a .net specific implementation, while float and double numbers can be processed by CPUs directly.
– codymanix
18 Answers
2396
votes
float and double are floating binary point types. In other words, they represent a number like this:
10001.10010110011
The binary number and the location of the binary point are both encoded within the value.
decimal is a floating decimal point type. In other words, they represent a number like this:
12345.65789
Again, the number and the location of the decimal point are both encoded within the value – that's what makes decimal still a floating point type instead of a fixed point type.
The important thing to note is that humans are used to representing non-integers in a decimal form, and expect exact results in decimal representations; not all decimal numbers are exactly representable in binary floating point – 0.1, for example – so if you use a binary floating point value you'll actually get an approximation to 0.1. You'll still get approximations when using a floating decimal point as well – the result of dividing 1 by 3 can't be exactly represented, for example.
As for what to use when:
For values which are "naturally exact decimals" it's good to use
decimal. This is usually suitable for any concepts invented by humans: financial values are the most obvious example, but there are others too. Consider the score given to divers or ice skaters, for example.For values which are more artefacts of nature which can't really be measured exactly anyway,
float/doubleare more appropriate. For example, scientific data would usually be represented in this form. Here, the original values won't be "decimally accurate" to start with, so it's not important for the expected results to maintain the "decimal accuracy". Floating binary point types are much faster to work with than decimals.
1132
votes
Precision is the main difference.
Float - 7 digits (32 bit)
Double-15-16 digits (64 bit)
Decimal -28-29 significant digits (128 bit)
Decimals have much higher precision and are usually used within financial applications that require a high degree of accuracy. Decimals are much slower (up to 20X times in some tests) than a double/float.
Decimals and Floats/Doubles cannot be compared without a cast whereas Floats and Doubles can. Decimals also allow the encoding or trailing zeros.
float flt = 1F/3;
double dbl = 1D/3;
decimal dcm = 1M/3;
Console.WriteLine("float: {0} double: {1} decimal: {2}", flt, dbl, dcm);
Result :
float: 0.3333333
double: 0.333333333333333
decimal: 0.3333333333333333333333333333
96
votes
+---------+----------------+---------+----------+---------------------------------------------------------+
| C# | .Net Framework | Signed? | Bytes | Possible Values |
| Type | (System) type | | Occupied | |
+---------+----------------+---------+----------+---------------------------------------------------------+
| sbyte | System.Sbyte | Yes | 1 | -128 to 127 |
| short | System.Int16 | Yes | 2 | -32,768 to 32,767 |
| int | System.Int32 | Yes | 4 | -2,147,483,648 to 2,147,483,647 |
| long | System.Int64 | Yes | 8 | -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
| byte | System.Byte | No | 1 | 0 to 255 |
| ushort | System.Uint16 | No | 2 | 0 to 65,535 |
| uint | System.UInt32 | No | 4 | 0 to 4,294,967,295 |
| ulong | System.Uint64 | No | 8 | 0 to 18,446,744,073,709,551,615 |
| float | System.Single | Yes | 4 | Approximately ±1.5e-45 to ±3.4e38 |
| | | | | with ~6-9 significant figures |
| double | System.Double | Yes | 8 | Approximately ±5.0e-324 to ±1.7e308 |
| | | | | with ~15-17 significant figures |
| decimal | System.Decimal | Yes | 16 | Approximately ±1.0e-28 to ±7.9e28 |
| | | | | with 28-29 significant figures |
| char | System.Char | N/A | 2 | Any Unicode character (16 bit) |
| bool | System.Boolean | N/A | 1 / 2 | true or false |
+---------+----------------+---------+----------+---------------------------------------------------------+
91
votes
The Decimal structure is strictly geared to financial calculations requiring accuracy, which are relatively intolerant of rounding. Decimals are not adequate for scientific applications, however, for several reasons:
- A certain loss of precision is acceptable in many scientific calculations because of the practical limits of the physical problem or artifact being measured. Loss of precision is not acceptable in finance.
- Decimal is much (much) slower than float and double for most operations, primarily because floating point operations are done in binary, whereas Decimal stuff is done in base 10 (i.e. floats and doubles are handled by the FPU hardware, such as MMX/SSE, whereas decimals are calculated in software).
- Decimal has an unacceptably smaller value range than double, despite the fact that it supports more digits of precision. Therefore, Decimal can't be used to represent many scientific values.
66
votes
I won't reiterate tons of good (and some bad) information already answered in other answers and comments, but I will answer your followup question with a tip:
When would someone use one of these?
Use decimal for counted values
Use float/double for measured values
Some examples:
money (do we count money or measure money?)
distance (do we count distance or measure distance? *)
scores (do we count scores or measure scores?)
We always count money and should never measure it. We usually measure distance. We often count scores.
* In some cases, what I would call nominal distance, we may indeed want to 'count' distance. For example, maybe we are dealing with country signs that show distances to cities, and we know that those distances never have more than one decimal digit (xxx.x km).
49
votes
float 7 digits of precision
double has about 15 digits of precision
decimal has about 28 digits of precision
If you need better accuracy, use double instead of float. In modern CPUs both data types have almost the same performance. The only benifit of using float is they take up less space. Practically matters only if you have got many of them.
I found this is interesting. What Every Computer Scientist Should Know About Floating-Point Arithmetic
39
votes
No one has mentioned that
In default settings, Floats (System.Single) and doubles (System.Double) will never use overflow checking while Decimal (System.Decimal) will always use overflow checking.
I mean
decimal myNumber = decimal.MaxValue;
myNumber += 1;
throws OverflowException.
But these do not:
float myNumber = float.MaxValue;
myNumber += 1;
&
double myNumber = double.MaxValue;
myNumber += 1;
28
votes
Integers, as was mentioned, are whole numbers. They can't store the point something, like .7, .42, and .007. If you need to store numbers that are not whole numbers, you need a different type of variable. You can use the double type or the float type. You set these types of variables up in exactly the same way: instead of using the word int, you type double or float. Like this:
float myFloat;
double myDouble;
(float is short for "floating point", and just means a number with a point something on the end.)
The difference between the two is in the size of the numbers that they can hold. For float, you can have up to 7 digits in your number. For doubles, you can have up to 16 digits. To be more precise, here's the official size:
float: 1.5 × 10^-45 to 3.4 × 10^38
double: 5.0 × 10^-324 to 1.7 × 10^308
float is a 32-bit number, and double is a 64-bit number.
Double click your new button to get at the code. Add the following three lines to your button code:
double myDouble;
myDouble = 0.007;
MessageBox.Show(myDouble.ToString());
Halt your program and return to the coding window. Change this line:
myDouble = 0.007;
myDouble = 12345678.1234567;
Run your programme and click your double button. The message box correctly displays the number. Add another number on the end, though, and C# will again round up or down. The moral is if you want accuracy, be careful of rounding!
26
votes
17
votes
13
votes
The Decimal, Double, and Float variable types are different in the way that they store the values. Precision is the main difference where float is a single precision (32 bit) floating point data type, double is a double precision (64 bit) floating point data type and decimal is a 128-bit floating point data type.
Float - 32 bit (7 digits)
Double - 64 bit (15-16 digits)
Decimal - 128 bit (28-29 significant digits)
More about...the difference between Decimal, Float and Double
11
votes
This has been an interesting thread for me, as today, we've just had a nasty little bug, concerning decimal having less precision than a float.
In our C# code, we are reading numeric values from an Excel spreadsheet, converting them into a decimal, then sending this decimal back to a Service to save into a SQL Server database.
Microsoft.Office.Interop.Excel.Range cell = …
object cellValue = cell.Value2;
if (cellValue != null)
{
decimal value = 0;
Decimal.TryParse(cellValue.ToString(), out value);
}
Now, for almost all of our Excel values, this worked beautifully. But for some, very small Excel values, using decimal.TryParse lost the value completely. One such example is
cellValue = 0.00006317592
Decimal.TryParse(cellValue.ToString(), out value); // would return 0
The solution, bizarrely, was to convert the Excel values into a double first, and then into a decimal:
Microsoft.Office.Interop.Excel.Range cell = …
object cellValue = cell.Value2;
if (cellValue != null)
{
double valueDouble = 0;
double.TryParse(cellValue.ToString(), out valueDouble);
decimal value = (decimal) valueDouble;
…
}
Even though double has less precision than a decimal, this actually ensured small numbers would still be recognised. For some reason, double.TryParse was actually able to retrieve such small numbers, whereas decimal.TryParse would set them to zero.
Odd. Very odd.
8
votes
For applications such as games and embedded systems where memory and performance are both critical, float is usually the numeric type of choice as it is faster and half the size of a double. Integers used to be the weapon of choice, but floating point performance has overtaken integer in modern processors. Decimal is right out!
5
votes
The problem with all these types is that a certain imprecision subsists AND that this problem can occur with small decimal numbers like in the following example
Dim fMean as Double = 1.18
Dim fDelta as Double = 0.08
Dim fLimit as Double = 1.1
If fMean - fDelta < fLimit Then
bLower = True
Else
bLower = False
End If
Question: Which value does bLower variable contain ?
Answer: On a 32 bit machine bLower contains TRUE !!!
If I replace Double by Decimal, bLower contains FALSE which is the good answer.
In double, the problem is that fMean-fDelta = 1.09999999999 that is lower that 1.1.
Caution: I think that same problem can certainly exists for other number because Decimal is only a double with higher precision and the precision has always a limit.
In fact, Double, Float and Decimal correspond to BINARY decimal in COBOL !
It is regrettable that other numeric types implemented in COBOL don't exist in .Net. For those that don't know COBOL, there exist in COBOL following numeric type
BINARY or COMP like float or double or decimal
PACKED-DECIMAL or COMP-3 (2 digit in 1 byte)
ZONED-DECIMAL (1 digit in 1 byte)
4
votes
In simple words:
- The Decimal, Double, and Float variable types are different in the way that they store the values.
- Precision is the main difference (Notice that this is not the single difference) where float is a single precision (32 bit) floating point data type, double is a double precision (64 bit) floating point data type and decimal is a 128-bit floating point data type.
- The summary table:
/==========================================================================================
Type Bits Have up to Approximate Range
/==========================================================================================
float 32 7 digits -3.4 × 10 ^ (38) to +3.4 × 10 ^ (38)
double 64 15-16 digits ±5.0 × 10 ^ (-324) to ±1.7 × 10 ^ (308)
decimal 128 28-29 significant digits ±7.9 x 10 ^ (28) or (1 to 10 ^ (28)
/==========================================================================================
3
votes
Decimal 128 bit (28-29 significant digits) In case of financial applications it is better to use Decimal types because it gives you a high level of accuracy and easy to avoid rounding errors Use decimal for non-integer math where precision is needed (e.g. money and currency)
Double 64 bit (15-16 digits) Double Types are probably the most normally used data type for real values, except handling money. Use double for non-integer math where the most precise answer isn't necessary.
Float 32 bit (7 digits) It is used mostly in graphic libraries because very high demands for processing powers, also used situations that can endure rounding errors.
Decimals are much slower than a double/float.
Decimals and Floats/Doubles cannot be compared without a cast whereas Floats and Doubles can.
Decimals also allow the encoding or trailing zeros.
2
votes
